Well, r/trees suggests an interesting business opportunity, but that's illegal. Lots of other subreddits (/r/mensrights, /r/politics, /r/worldnews, /r/atheism) are hotbeds of demagoguery and outrage, which may be good for political fundraising but little else. (It's possible to sell demagoguery and outrage--Rupert Murdoch and Arianna Huffington have taught us that much--but I don't know about selling it people who are already getting it for free.) And then of course, pictures of cats and formulaic jokes are another thing.